The present invention relates to a variable valve timing control apparatus of an internal combustion engine, which variably controls open and closing timing of an intake valve and/or an exhaust valve of the engine in accordance with an engine operating condition.
As a related art variable valve timing control apparatus of an internal combustion engine, Japanese Unexamined Patent Application Publication No. 2013-36390 (hereinafter is referred to as “JP2013-36390”) discloses a variable valve timing control apparatus applied at an intake valve side.
The variable valve timing control apparatus of JP2013-36390 has a timing sprocket to which a turning force is transferred from a crankshaft of an engine, a front plate which closes or covers a front opening of a cylindrical housing of the timing sprocket, a vane rotor which is rotatably housed in the housing and defines a retard working chamber and an advance working chamber in the housing, and a cover portion which is set, at a front end side of the front plate, spaced a slight distance apart from the front plate and whose crank-shaped middle part is fixed to the vane rotor. The variable valve timing control apparatus further has a spiral spring which is provided between the cover portion and the front plate, and whose one end is engaged with an outer circumferential portion side of the front plate and whose other end is engaged with a middle portion (a rotational bush) of the cover portion so as to wind around an outer circumferential surface of the middle portion (the rotational bush) of the cover portion.
The spiral spring forces the vane rotor by a spring force so that the vane rotor relatively rotates to an advanced angle side with respect to the timing sprocket. By controlling the intake valve open/closing timing to the advanced angle side, engine startability can be improved.
Further, the cover portion is formed so as to avoid the spiral spring being disengaged with the cover portion and coming off to a front side when the spiral spring is deformed (a shape of the spiral spring is changed) in a spiral widening direction or a spiral shrinking direction.